#include <iostream.h>
and #include <fstream.h>
ifstream inData;
ofstream outData;
inData.open("file_input.txt");
outData.open("file_output.txt");
if (!inData) { cout << "** Problem: cannot open file_input.txt, ending program." << endl; return 1; }Note that this step is not mandatory, but it is good programming practice.
inData >> inVar1 >> inVar2;
outData << inVar1;
The following C++ program illustrates file I/O with simple error checks after the open statements.
/**************************************************** * * FileName: ~ftp/pub/class/cplusplus/Csyntax-files/Cpgms/file_io.cpp * Author: Ada Lovelace * Purpose: * Demonstrate simple file I/O * ********************************************************/ #include <iostream.h> #include <fstream.h> #include <string> using namespace std; int main() { ifstream inData; ofstream outData; string inVar1; string inVar2; cout << endl << "This program reads from an input file, file_input.txt," << endl << " and writes to an output file, file_output.txt" << endl; inData.open("file_input.txt"); if (!inData) { cout << "** Problem: cannot open file_input.txt, ending program." << endl; return 1; } outData.open("file_output.txt"); if (!outData) { cout << "** Problem: cannot open file_output.txt, ending program." << endl; return 1; } inData >> inVar1 >> inVar2; while ( inData) { outData << inVar2; // output in reverse order outData << " "; outData << inVar1; outData << endl; inData >> inVar1 >> inVar2; } // end while inData.close(); outData.close(); } // end main
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Copyright 2000 Department of Computer Science, University of Regina.